1. Field of the Invention
The present invention relates to an image heating apparatus that heats an image on a recording material. The image heating apparatus can be used in an image forming apparatus, such as a copy machine, a printer, a facsimile machine and a complex machine with a plurality of functions of these devices.
2. Description of the Related Art
Conventionally, an image forming apparatus, such as a copying machine, includes a fixing apparatus (image heating apparatus) that fixes a toner image formed on recording paper (recording material). In recent years, quick start of printing, more specifically, quick completion of image formation on a first recording paper after reception of a print command (quick start property), is demanded. Therefore, the heat capacity of a fixing member (endless belt) is reduced.
When the fixing member with reduced heat capacity is used, the temperature of an area as a paper non-passing section of the fixing member may be excessively increased in a fixing process (image heating process) on recording paper narrower than recording paper with a maximum width that can be used for the apparatus.
For handling the problem, although the fixing member with reduced heat capacity is not used, an apparatus described in Japanese Patent Application Laid-Open No. 2010-002488 includes a heat pipe (heat absorption rotary member) arranged in contact with a pressure roller. Specifically, the apparatus described in Japanese Patent Application Laid-Open No. 2010-002488 uses a heat transport function in a direction of axis of the heat pipe to equalize a temperature distribution in the direction of axis of the pressure roller. In this way, an attempt is made to indirectly prevent an increase in the temperature of the paper non-passing section of the fixing roller.
However, if the heat pipe is continuously in contact with the pressure roller as in the apparatus described in Japanese Patent Application Laid-Open No. 2010-002488, it is difficult to increase the temperature of the fixing roller and the pressure roller to a desired fixing temperature in a short time. More specifically, the time required for warm-up of the fixing apparatus is long, and quick start of printing is difficult. This is because the heat capacity of the heat pipe arranged to handle the increase in the temperature of the paper non-passing section is large, and the heat capacity cannot be ignored. More specifically, heat flows to the heat pipe through the pressure roller during warm-up, and the fixing roller and the pressure roller are in a relationship in which an increase in the temperature to the desired fixing temperature is difficult.